Hi, I just had to respond to this. I think this is probably always going to be a concern for those of us with pku. I sometimes drink an extra formula. I often find that I get really hungry after a workout- weights, cyxling, or whatever else. My dietician says I shouldn’t be hungry but I always am. I think you just have to do like a science experiment to try to find what works for you. I’ve found that weights in combination with some type of aerobic thing ( for me it’s swimming because I have asthma) helps. It’s probably always going to be a puzzle to tery to figure out how we can do what other people seem to just do naturally( bulid muscle) It took me about 6 months of intense weight training ( 3 sets 15-25 reps) to finally get to where I can see some muscle beginning to show up. Good luck and let me know if it works.